Recently, along with change in residential environment, there has been an increasing demand to remove harmful airborne substance such as pollen and mites causing humane allergic diseases, to realize more healthy and comfortable life. In order to meet such a demand, air conditioning apparatuses with various filters have been developed, as described, for example, in Japanese Patent Laying-Open Nos. 6-154298, 7-807, 8-173843 and 2000-111106.
These air conditioning apparatuses are of the type that absorb or filter harmful airborne substance by sucking in air in the space through a filter. Therefore, such apparatuses inherently necessitate maintenance such as filter exchange for use over a long period of time, and in addition, satisfactory performance can not always be attained because of insufficient properties of the filter.
Though prevention through vaccination has been proposed, it is not always effective, as the amount and quality for immunization differ one person to another.
Therefore, an effective method of suppressing allergic disease without such disadvantage or difficulty has not been known to date.